Politicians supporting Sheldon Adelson’s proposed online gambling ban claim to want to protect the poor and children and to prevent crime. But if they truly cared about these issues rather than getting in Mr. Adelson’s good graces, they would reject such a ban.

A ban on a good or service for which there is demand simply pushes people into the black market, creating a host of unintended consequences that make consumers less safe. Dozens of other countries have had legal online gambling for decades with few negative consequences. And there are many technological methods for verifying a player’s age, identity and location.

In fact, two of Mr. Adelson’s casinos — the Venetian and the Palazzo — offer a mobile gambling app that allows players to use their smartphones to bet on sporting events from anywhere in Nevada. As with buying lottery tickets, the decision to gamble online ought to be left up to individuals. Its regulation ought to be decided by the states, not Congress — and certainly not by a casino magnate.